During 2006, approximately 30% of adults reported experiencing some type of joint pain during the preceding 30 days. Knee pain was reported by 18% of respondents, followed by shoulder pain (9%), finger pain (7%), and hip pain (7%). Joint pain can be caused by osteoarthritis; injury; prolonged, abnormal posture; or repetitive motion. According to the American Academy of Orthopaedic Surgeons, about 4 million people in the United States seek medical care each year for shoulder sprain, strain, dislocation, or other problems. Each year, shoulder problems account for about 1.5 million visits to orthopaedic surgeons.
Shoulder pain is prevalent among people of advanced age and those who suffer from rheumatoid arthritis, spinal cord injury, stroke, and Parkinson's disease. An important detail that distinguishes shoulder pain from other forms of musculo skeletal pain is the prevalence of sleep related symptoms. A plethora of clinical studies have shown that nocturnal pain, insomnia, and inability to sleep on the affected side are prominent features of shoulder pain. Furthermore, patients sometimes report that they experience shoulder pain for the first time when they wake up at night or in the morning, without prior warning or a specific inciting event.
Most commonly, shoulder pain is associated with trauma or overuse. However, the overuse theory cannot explain adequately the occurrence of shoulder pain in those who do not engage in activities that involve repeated and stressful use of the shoulder, since the percentage of the painful right shoulders usually does not match the percentage of dominant right arms in such individuals. An alternative hypothesis, well substantiated by statistical evidence, has linked shoulder pain to postural immobility in the decubitus position (J. Zenian, Sleep Position and Shoulder Pain. Medical Hypotheses, 2010, volume 74, page 639-643). Indeed, prolonged pressure on the shoulder caused by the weight of the thorax can produce enough damage to cause subsequent shoulder pain. Furthermore, infraspinatus, and posterior deltoid muscles of both shoulders (in contact with the bed and the opposite) become overstretched and cause pain (J. Travell, D. Simons, L. Simons; 1999, Myofascial Pain and Dysfunction: The Trigger Point Manual. USA: Lippincott Williams & Williams. ISBN 0-683-08363-5). Many shoulder pain sufferers find sleeping on the side painful. The intense pressure exacerbates shoulder pain, interferes with sleep, and can lead to soreness in the neck and arm, as well as numbness in the involved extremity. Some shoulder pain sufferers resort to sleeping on their backs, and, as a consequence, experience apnea. There is a significant body of evidence demonstrating that for many snorers, both non-obstructive and obstructive sleep apnea is position-specific and occurs while sleeping on the back. Sleeping in a semi-seated position or in a lateral decubitus position prevents snoring for these patients and both simple (e.g., sewing a tennis ball to the back of pajamas, sleeping in a recliner) and complex (H. Loord, E. Hultcrantz. Positioner—a method for preventing sleep apnea. Acta Oto-Laryngologica, 2007; 127: 861-868) methods to prevent back sleeping are recommended. Commonly suggested solutions for minimizing the impact on shoulders while side sleeping include high pillows, a thick blanket tacked under the torso so that a gap for placing the shoulder (between the pillow and blanket) is formed. Some sleepers find sleeping on a couch, with the back leaning against the back of the couch, more comfortable. Those who sleep on their sides often experience chronic neck and back pain due to spinal misalignment.